By Judith Ireland and James Massola

UpdatedApril 30, 2015 — 5.20pmfirst published at 2.40pm

Labor leader Bill Shorten has sent a clear signal that he does not agree with deputy leader Tanya Plibersek's push for the ALP to have a binding vote on same-sex marriage, highlighting a clear split in the party's leadership.

And some in Ms Plibersek's own Left faction have now abandoned the Deputy Opposition Leader and distanced themselves from the proposal, ensuring it will almost certainly be defeated at Labor's national conference.

It comes as another stoush deepened over the new presidency of the ALP, putting the national Left and the Victorian Left factions at odds.

On Thursday, when asked about his position on same-sex marriage, Mr Shorten said that while Australia had waited too long for the reform, "the best way to achieve it ... is not to force people to agree with it, but to convince them".

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Tanya Plibersek says Labor should change its platform on same-sex marriage at its national conference in July.Credit:Andrew Meares

"These are matters that will be discussed at the national conference. Bill's position, I think, has been articulated and carried by the last national conference and I'd be very surprised if the position that he's taken at this conference will be any different," he said.

Labor operatives from the Left and the Right factions seized on those comments as proof the Left had split on the issue, meaning there was no chance Ms Plibersek's proposal would succeed.

"I'd be very surprised if there was a different outcome from the last conference. We won't embarrass Shorten or try to enforce an unenforceable position," one senior member of the Left said.

Ms Plibersek's move has been met with passionate criticism from some quarters of the party, with some MPs threatening to cross the floor if they were made to support same-sex marriage. Others are angry at what they perceive to be leadership manoeuvring by the ALP's deputy leader.

When asked by reporters if he thought Ms Plibersek had raised the issue while he was overseas to boost her own popularity, Mr Shorten replied: "Not at all."

Mr Shorten is on the record as supporting a conscience vote and said again on Thursday he would like to see a conscience vote rather than a binding one.

While Mr Shorten also noted that Ms Plibersek had previously supported a binding vote (she voted for one at the ALP's 2011 national conference), his own remarks reinforce the stark contrast between their views on same-sex marriage strategy.

The Labor frontbench is split on the conscience vote idea.

Other members of the Left such as Penny Wong, Mark Butler, Jenny Macklin and Stephen Jones, support a binding vote but senior Left faction leader Anthony Albanese, has previously supported a conscience vote and is said to still do so.

Members of the Right (which includes Mr Shorten), as well as Joel Fitzgibbon and David Feeney, support a conscience vote.

A factional war is also breaking out over the next Labor president, which will be decided in a ballot that opens in about two weeks.

The Left faction members of the ALP's national executive met on Monday to endorse shadow minister Mr Butler for the position. But the Victorian Left is furious Mr Butler, who already has a national profile, is standing for the role. On Tuesday, the Victorian Left faction executive met and chose to back one of their own - Victorian state government minister Jane Garrett, a current national vice-president.

A resolution adopted by the Victorian Left meeting lashed the national executive's decision as "undemocratic, counterproductive and against the spirit of the national presidency ballot".

About 10,000 members are expected to vote in the national presidency.

In effect, the contest pits against each other two of the Left's most senior figures: Anthony Albanese, a supporter of Mr Butler, and Kim Carr, who is promoting Ms Garrett.

To further complicate the already messy five-candidate race, former WA senator Louise Pratt is running as a third candidate for the Left faction.

Some on the Left now fear that with the vote potentially split three ways, Mr Shorten's preferred Right faction candidate – the little known Tim Hammond – could slip through the middle and get elected.